Circulating Sub with Activation Mechanism and a Method Thereof

ABSTRACT

The present invention relates to an activation method, an activation mechanism and a downhole tool comprising the activation mechanism. The activation mechanism com-prises a pressure switch for turning power to the electrical components, a control unit connected to a pressure sensor for sensing the internal pressure of the drilling fluid located in a first fluid conduit. The control unit controls an actuator unit connected to a moveable valve element. The actuator unit moves the valve element from a closed position when activated. A seat for the valve element is arranged relative to a second fluid conduit so that the valve element closes the second conduit when it is placed in its seat. This provides a very fast and accurate activation method that involves the use of balls or RFID tags. Furthermore, the downhole tool can be activated even if no actual flow is passing through the tool.

FIELD OF THE INVENTION

The present invention relates to an activation mechanism for activating a circulating sub in a drill string, comprising a sensor sensing at least a pressure of a drilling fluid located in a first fluid conduit in the downhole tool when installed, a valve element arranged relative to a second fluid conduit in the downhole tool when installed, and a control unit connected to the sensor and configured to monitor the sensed signal and to electronically control the movement of the valve element based on the sensed signal.

The present invention also relates to a circulating sub for positioning in a borehole, comprising a housing having an outer side surface facing an inner wall of the borehole, a first fluid conduit connected to a first opening in one end and a second opening in the other end for leading a drilling fluid through the circulating sub, and at least a second fluid conduit in fluid communication with the first fluid conduit, wherein the circulating sub further comprises an activation mechanism as mentioned.

The present invention finally relates to a method for activating a circulating sub using an activation mechanism as mentioned above, where the method comprises the steps of positioning the circulating sub at a predetermined depth of a borehole, increasing a pressure of a drilling fluid located in the first fluid conduit of the circulating sub, monitoring the pressure of the drilling fluid inside the first fluid conduit, and activating the circulating sub when a certain event is detected using a control unit.

BACKGROUND OF THE INVENTION

Today, various activation systems are used to selectively activate downhole tools, such as circulating subs, under-reamers and other types of downhole tools used during drilling operations. It is known to drop balls of various sizes into the drilling fluid to activate or deactivate a circulating sub having a corresponding number of ball retainers for receiving these balls. Such an activation system only has a limited number of activations/deactivations, typically between five to seven times, and determined by the size of the ball retainers. Once full, the circulating sub must be retrieved and the ball retainers emptied before it can be lowered into the drilling hole again. Furthermore, the ball may be stopped in the fluid passageway by accumulated solid particles, thereby blocking the circulation of drilling fluid and causing an increase in pressure above the blockage which could damage the downhole tool or even the operation equipment located at ground level.

Another activation system solving this problem uses a radio frequency (RF) receiver or transceiver arranged in the circulating sub to wireles sly communicate with one or more radio frequency identification (RFID) tags being dropped into the drilling fluid. Once within communication range of the receiver/transceiver, the RFID device is able to communicate with the circulating sub for activating or deactivating a selected circulating sub. An exemplary solution thereof is disclosed in US 2013/0319767 A1 wherein active or passive RFID tags are used to activate a desired function of the circulating sub based on the command received from the RFID tag. A pressure sensor in the circulating sub can be used instead to detect mud pulses or flow rate signals for activating the circulating sub.

Both types of activation systems provide a slow and time consuming process since each ball or RFID tag first has to be pumped via the drilling fluid from the ground level to the selected downhole tool before the downhole tool can be activated or deactivated. It often takes more than one hour for the RFID tag or ball to reach a downhole tool located at a depth of about 3000 metres as the speed by which the RFID tag or ball travels depends on the pumping speed and the internal diameter of the drilling string.

Yet another solution is to use an indexing type activation system in which the mode of the downhole tool is changed every time the pumps circulating the drilling fluid are turned off and on. The disadvantage of this solution is that the sequence of modes is determined by the indexing mechanism, thus the operator must follow the indexing sequence to select a desired mode. Furthermore, it is well known that such indexing mechanisms have a complex configuration that is prone to mechanical failures.

WO 2013/103907 A1 discloses an under-reamer having a pressure activated flow switch mechanism for activating and deactivating the under-reamer. The flow switch mechanism comprises a piston configured to move between an open position and a closed position based on the different pressures. A spring element pushes the piston towards an upper seat of the housing to form a seal in the closed position. Once the differential pressure of the passing drilling fluid exceeds the spring force, the piston is axially moved to the open position where it contacts a lower seat of the housing. Thereby, allowing drilling fluid to enter an upper chamber while drilling fluid is ventilated from a lower chamber out through an outer opening. The drilling fluid in the upper chamber further acts on another piston which radially moves the cutting block out of the housing. The spring element forces the piston back to the closed position when the spring force exceeds the combined forces of the differential pressure and the friction of an annular seal located between the piston and the surrounding housing. This activation mechanism has a complex configuration and requires an actual flow through the under-reamer tool for activating the cutting block.

There is a need for providing an improved method that allows for a fast and accurate activation of a downhole tool, such as a circulating sub, without the use of a ball or RFID tag or a complicated downhole link.

US 2013/0284424 A1 discloses a circulating sub comprising a housing having a central fluid path in fluid communication with a bypass path in the sidewall of the housing. The bypass path has an inlet opening facing the central fluid path and an outlet opening facing the annulus surround the sub. A moveable piston is arranged inside an interior chamber relative to this bypass path and comprises a plug facing a plug seat located in the bypass path. A pressure sensor is used by a controller in the interior chamber to detect an activation signal via mud pulses or downlink signals transferred through the passing mud in the central fluid path. Upon activation, the controller ignites a combustible agent wherein the combustion gasses push the piston into the bypass path until the plug comes into contact with the plug seat. This closes off the bypass path. This configuration provides a single-use activation after which the circulating sub must be retrieved from the borehole and reset. This activation mechanism can only be accessed and reset by taking the sub apart which adds to the complexity and costs of the sub.

OBJECT OF THE INVENTION

An object of this invention is to provide an activation mechanism that overcomes the drawbacks of the prior art.

An object of this invention is to provide an activation mechanism that allows for a fast and accurate activation of a downhole tool.

An object of this invention is to provide an activation mechanism capable of activating the downhole tool without an actual flow of drilling fluid.

An object of the invention is to provide a downhole tool with an integrated activation mechanism that reduces the risk of a seal failing during operation.

DESCRIPTION OF THE INVENTION

An object of the invention is achieved by an activation mechanism for activating a circulating sub in a drill string, comprising:

-   -   at least one sensor configured to sense at least a pressure of a         drilling fluid located in a first fluid conduit in the         circulating sub when installed,     -   a control unit connected to the sensor and configured to monitor         the sensed signal of the at least one sensor, wherein the         control unit is configured to electronically activate the         movement of at least one moveable valve element in one direction         based on the sensed signal,     -   wherein the at least one valve element is configured to be         arranged relative to at least a second fluid conduit in the         circulating sub when installed, the at least one valve element         is configured to move between an open position and a closed         position,     -   wherein the second fluid conduit is in fluid communication with         the first fluid conduit, and the at least one valve element         comprises at least one valve end configured to close the second         fluid conduit in the closed position and to open the second         fluid conduit in the open position, characterised in that     -   the control unit is electrically connected to at least one         actuator unit arranged relative to the at least one valve         element, the at least one actuator unit is configured to perform         a reciprocating movement of the at least one valve element         between the open position and the closed position, wherein the         control unit is further configured to electronically activate         the movement of the at least one moveable valve element in an         opposite direction.

The term “close” means that the valve element is moved into the conduit and substantially blocks off (shut) the fluid passageway so that no drilling fluid can flow through the conduit. The term “open” means that the valve element is moved out of the conduit so that the drilling fluid can flow through the conduit again.

This provides a simple and accurate activation mechanism that does not require a ball or RFID tag to be dropped into the drilling fluid for activating or deactivating the downhole tool. This allows for a very fast activation/deactivation process compared to activation systems using a ball or RFID tag. In example, this configuration allows a downhole tool located at a depth of about 3000 metres to be activated within a few minutes, e.g. about three minutes. Furthermore, no indexing systems are needed to select an operation mode of the downhole tool, as the operation mode can be selected during the start-up process of the pumping system, thus no cycling between start and stop of the pumping system is needed to select the operation mode.

This configuration allows the activation mechanism to be integrated into the downhole tool or arranged as a standalone unit configured to be connected to the downhole tool. This configuration is well-suited for any type of circulating subs in which a bypass of the main fluid flow is desired. The drilling fluid may be any type of air, mist, foam, inert gas, or even any mixture or combination of different gravity fluids or gasses.

The control unit is configured to control the actuator unit, e.g. first actuator unit, which in turn moves the valve element, e.g. first valve element, forwards or backwards along a predetermined direction. The direction of movement may be parallel and/or orthogonal to the axial/longitudinal direction of the downhole tool. Any type of actuator unit may be used to move the valve element, e.g. a linear actuator, a piston or another suitable actuator unit. The actuator unit may be powered by an electrical, mechanical or hydraulic power unit integrated into or connected to the control unit. This allows the control unit to control the movement and/or speed of the valve element.

In one embodiment, the control unit is further configured to apply at least a first time window to the sensed signal and to determine whether the sensed signal remains stable relative to at least a first threshold value within the at least first time window or not, wherein the at least one valve element is activated if a stable pressure level is detected.

The terms “stable”, “stable level” and “stable pressure level” are defined by a predetermined threshold level or band having an upper and a lower limit value centred relative to the threshold value where the sensed parameter, e.g. the pressure, remains within the upper and lower limit values for at least the during of the time window.

The control unit may be any type of analogue, digital or logical electronic circuit suitable of processing and monitoring the electrical signals received from the sensors, e.g. the pressure sensor. Alternatively, another type of sensor may be used to detect a signal representative of the pressure of the drilling fluid. In a preferred configuration, the control unit comprises a controller, e.g. a microprocessor, configured to at least monitor the sensed pressure within a predetermined/first time window. The control unit/controller is further configured to compare the sensed pressure with at least one/first threshold value defining at least one/first operation mode. This operation mode may simply be to activate or deactivate the downhole tool. The control unit/controller is configured to determine whether the pressure of the drilling fluid remains stable within the first time window, i.e. within the upper and lower limit values of the respective threshold value. If a stable level is detected, then the control unit/controller sends a predetermined control signal or command to the downhole tool for activation/deactivation of the tool or selection of an operation mode thereof. The control signal may simply be used to activate the actuator unit which then moves the valve element in the forward or backward direction depending on the respective control signal. The detection of a stable level of the sensed parameter allows a simpler and less complex activation process compared to downhole link systems using mud pulses or even flow pulses.

The time window may be selected based on the operating flow rate, the operating pressure or the dimensions of the borehole. The upper and lower limits may be determined based on the respective threshold value and/or the tolerance of the pumping system. The operating pressure may be selected between 10 bar and 100 bar. The time windows may be selected between 1 minute and 10 minutes, e.g. between 3 minutes and 5 minutes. The upper and lower limit values may be selected between ±1% to ±10% of the selected activation level/threshold value or the operating level.

In one embodiment, the control unit is further configured to apply at least a second time window to the sensed signal, and the control unit is further configured to determine whether the sensed signal remains stable relative to at least a second threshold value within the at least second time window or not.

In this configuration, the control unit/controller is configured to compare the sensed pressure to two or more threshold values each defining an operation mode of the same downhole tool or an activation level for individual downhole tools. The individual downhole tools may be connected to the same activation mechanism or, alternatively, to individual activation mechanisms each designed for a selected threshold value. The individual downhole tools may further have the same configuration or different configurations depending on the desired application and/or position in the borehole. This allows multiple operation modes and/or downhole tools to be activated or deactivated via the activation mechanism.

The second time window may be the same as the first window or have a different length and/or shape. The second threshold value may be the same as the first threshold value or have a value that is higher or lower than the first threshold value. The limit values for the first and second threshold values may be the same or they may differ for each threshold value, e.g. define different threshold ranges. This allows the activation levels to be optimised for each downhole tool and/or each operation mode for enatiling a better control of multiple operation modes and downhole tools.

The two or more threshold values may be used to simply control the actuator unit which selectively extend or retract the valve element, e.g. selectively closes or opens the second fluid conduit, dependent on the sensed pressure. In this configuration, the controller may monitor the sensed signal, e.g. within another predetermined time window, and selective activate the actuator unit each time the sensed pressure reaches one of the threshold values. The actuator unit in turn performs a reciprocating movement of the valve element according to this selective activation. The control unit may optionally comprise a timer unit electrically connected to the controller, wherein the timer unit may be activated when the valve element is moved into the open or closed position. Once a predetermined time period has lapsed, then the controller may via the actuator unit move the valve element back into the closed or open position. This enables the circulating cub to be activated at regular intervals, if needed, to provide a pulsating fluid flow in the annular space. This pulsating flow may also be used to dis-lodge or remove any accumulated cuttings in the annular space.

The control unit/controller may further be configured to detect a temporary drop or reduction in the sensed signal, e.g. the sensed pressure. The drop or reduction may be defined by a predetermined amplitude and/or time length. This allows the control unit to verify that the selected downhole tool or operation mode has been activated or deactivated. The second time window may be applied after this temporary drop or reduction has been detected, or after the pumping pressure has been increased or lowered to the second threshold value.

In exemplary embodiment, the actuator unit comprises at least one solenoid element for inductively moving at least one push rod mechanically connected to the at least one valve element.

The actuator unit preferably comprises a solenoid element for inductively moving a magnetic or magnetic conductive rod or tube, i.e. a push rod, which in turn is mechanically connected to the valve element. The solenoid element is arranged relative to the push rod so that a magnetic field is directed into the material, e.g. steel or a ferromagnetic material, of the push rod. The push rod may form part of the valve element. An external or internal power unit, e.g. a battery, may be used to supply the solenoid. Dependent on the direction of the current flow in the windings of the solenoid, the solenoid may move the valve element in one or both directions and thus towards the open and/or closed position. The control unit/controller may adjust the current level in the solenoid which in turn regulates the speed of the valve element. This allows for a simple and quick movement of the valve element using a minimum of components. This also provides a better control of the movement compared to other activation mechanism using combustible agents.

Optionally, a spring element may be arranged relative to the push rod for biasing the movement towards the closed position. This provides a failure safe function to the activation mechanism in which the valve element is held in the closed position so no drilling fluid is led through the second fluid conduit.

In one embodiment, at least one sealing element is arranged in an outer surface of the poppet valve, the outer surface is facing an inner surface of the chamber, wherein the at least one sealing element remains in contact with the inner surface during movement of the poppet valve.

The valve element is positioned inside a chamber, e.g. a first chamber, formed in the activation mechanism or in the downhole tool where the valve element is able to move relative to the chamber when activated. The chamber may be formed in a sidewall of the housing of the downhole tool. The valve element is preferably formed as a poppet valve where one end is connected to or form part of the push rod mentioned above. The valve element may be a solid or hollow element with no internal fluid conduits or openings. The other end of the valve element/poppet valve is shaped to be brought into contact with a seat, e.g. a valve seat, located relative to the second fluid conduit, e.g. a branch thereof. This valve end is configured to substantially close the second fluid conduit when placed in the seat, e.g. the closed position.

The chamber comprises at least one inner surface facing a corresponding outer surface of the valve element. The chamber further has a first end facing the second fluid conduit and a second end facing away from the second fluid conduit. The sealing elements, e.g. one, two or more, are arranged in a dedicated outer surface of the valve element/poppet valve and contact a dedicated inner surface of the chamber. The sealing element may be O-rings, GT-rings or any other suitable sealing element. This allows the sealing elements to remain in contact with this inner surface at all times during the movement, thus forming a continuous seal preventing drilling fluid from entering the chamber. This reduces the risk of the sealing element failing compared to conventional downhole units, since no peripheral edges of the valve element are moved past the sealing elements, nor is the sealing elements moved past any peripheral edge of a bypass opening in the housing.

In conventional downhole tools, a bypass conduit in the housing matches a corresponding bypass opening provided in the body of the centrally placed valve or sleeve. Drilling fluid is guided through the sleeve or valve and out through this bypass opening and further through the bypass conduit of the housing. Sealing elements located on the housing or on the valve or sleeve seal off the area between these two units. During movement, the valve or sleeve is moved relative to the housing so that the peripheral edge of the bypass conduit or bypass opening is moved past one or more of the sealing elements. This increases the risk of the respective sealing element failing due to increased wear; the peripheral edge may even force the respective sealing element out of its seat. The present invention solves this problem by placing the activation mechanism and thus the valve element in the sidewall of the housing so no fluid conduits in the valve element are needed.

At least a second valve element may be arranged in the first chamber or in at least a second chamber. The second valve element may be arranged relative to the second fluid conduit, e.g. another branch thereof, or at least another/third fluid conduit in fluid communication with the first fluid conduit. Optionally, a second actuator unit may be connected to the second valve element for moving that valve element where this actuator unit is controlled by the control unit/controller. The at least two valve elements and actuator units may have the same configuration or different configurations.

The individual valve elements may be activated at the same pressure level or at different pressure levels. This allows the activation mechanism to control the fluid bypass of two or more fluid conduits, thus allowing for an improved control of the bypass of the drilling fluid.

Alternatively, the first valve element as described above may be arranged relative to two or more branches of the second fluid conduit and/or two or more fluid conduits in fluid communication with the first fluid conduit. This allows for an increased bypass of the drilling fluid. The individual branches and/or fluid conduits used to bypass the drilling fluid are designed to reduce any ‘dead end’ areas between the respective inner and outer openings. In example, the seat may be positioned parallel or perpendicular to the flow direction in the branch/conduit. The side or sides of the seat may be sloped or curved and/or have a minimal surface area to prevent solids from accumulating on the seat which otherwise would render the valve element inoperable. The internal surfaces of the branch/conduit and optionally the seat are preferably shaped so that they do not form any significant or large restrictions along the flow path which otherwise would cause an increase in the flow velocity and, thus, an accelerated wear.

In one embodiment, a valve housing is arranged inside the chamber, wherein the poppet valve extend at least partly into the valve housing via an opening in one end of the valve housing.

The chamber may comprise a narrow portion and a large portion. The narrow portion, e.g. an internal hole, is at one end in communication with the second fluid conduit. The narrow portion is at the other end in communication with the large portion. The inner dimensions of the narrow portion substantially correspond to the outer dimensions of the valve element, thus forming a relative tight fit around the valve element. This increases the structural strength of the sidewall of the housing near the second fluid conduit as only a minimum amount of material is removed. The large portion, e.g. a cavity having an opening located in an outer side surface of the sidewall, is configured to receive and hold the remaining components of the activation mechanism.

A valve housing or retainer may be arranged in the chamber, e.g. in the large portion, and comprises one end facing the second fluid conduit and another end facing the actuator unit. The push rod may extend at least partly into the valve housing via an opening in this other end. This opening may be sealed off using suitable sealing means. The valve element/poppet valve may also extend at least partly into the valve housing via an opening in this one end. This opening may be also sealed off using suitable sealing means. The valve housing may be partly or fully filled with a lubricant, e.g. oil. This reduces the amount of air inside the valve housing and reduces the energy required to move the valve element. This also keeps the sealing elements intact.

The valve housing may comprise guiding means, e.g. a bearing, for guiding the valve element is it moves relative to the valve housing. When placed in the closed position, a contact surface on the valve element, e.g. a thickened or thinned portion, is optionally brought into contact with a corresponding contact surface on the valve housing, e.g. a protrusion. Likewise when placed in the open position, a contact surface on the valve element, e.g. a thickened or thinned portion, is optionally brought into contact with a corresponding contact surface on the valve housing, e.g. a protrusion. This limits the movement of the valve element relative to the valve housing.

Alternatively, the push rod may be connected to this other end of the valve housing and thus the valve housing may be moved relative to the chamber. As the valve housing is moved towards the second fluid conduit, a contact surface on the valve housing may be brought into contact with a corresponding contact surface on the valve element. The valve housing and valve element are then moved together towards the closed position Likewise, as the valve housing is moved away the second fluid conduit, another contact surface on the valve housing may be brought into contact with another corresponding contact surface on the valve element. The valve housing and valve element are then moved together towards the open position.

In one embodiment, the control unit is further connected to an activation circuit, e.g. a pressure switch, which is configured to activate the control unit at a predetermined pressure level.

The control unit is electrically connected to an activation circuit for reducing the power consumption of the electrical components. The activation circuit is configured to wake up the control unit, e.g. turn power on, when the pressure inside the first fluid conduit exceeds a predetermined/third threshold level. Any suitable activation circuit may be used to wake up the control unit, such as a simple pressure switch. The control unit/controller then monitors the internal pressure of the drilling fluid in the first fluid conduit and activates a desired operation mode or downhole tool or the actuator unit as described above if a stable pressure level is detected. Once the activation circuit determines, e.g. simply by detection, that the pressure drops below the third threshold value, the control unit enters a sleep mode, e.g. power is turned off. This allows the control unit to only be activated when the internal pressure of the drilling fluid reaches a predetermined pressure level, thus reducing the power consumption and increasing the operation time.

The control unit may also be configured to enter sleep mode after completing one or more task, such as activation of the selected operation mode or downhole tool and optionally verifying the activation as described above. The control unit may be further configured to activate the downhole tool or actuator unit when a certain event is detected, such as excessive vibrations or cocking of a jarring tool.

In one embodiment, the activation mechanism is configured to be implemented in a cavity located in an outer side surface of a housing of the circulating sub.

The activation mechanism according to the invention has a small enough configuration for implementation or installation in an outer cavity located in the housing of the downhole tool, while most conventional activation mechanisms are designed for implementation/installation in a central cavity of the downhole tool. This allows for a more optimal fluid passageway in the central through hole, i.e. the first fluid conduit, of the downhole tool, since there are no flow restrictions or at least a reduced number of flow restrictions in the downhole tool. Also, this provides quick and easy access to the various components of the activation mechanism whereas other activation mechanisms are only accessible by taking the entire downhole tool apart.

In one embodiment, the at least one sensor comprises a first sensor configured to sense a first pressure of the drilling fluid in the first fluid conduit and a second sensor configured to sense a second pressure of the drilling fluid in a returning drilling fluid when installed, wherein the control unit is configured to determine a differential pressure by using the first and second pressures.

The activation mechanism may comprise at least two pressure sensors electrically connected to the control unit/controller. A first pressure sensor is arranged relative to the first fluid conduit for measuring an internal/first pressure of the drilling fluid, e.g. via an opening in the inner surface of the through hole. A second pressure sensor is arranged relative to the annulus for measuring an external/second pressure of the returning drilling fluid, e.g. via an opening in the outer side surface of the housing or in the removable cover. The control unit may be configured to determine a differential pressure using the pressure signals from the first and second pressure sensors. The differential pressure may be compared to a predetermined threshold value, e.g. between 40 bar and 60 bar, e.g. 50 bar. If the measured differential pressure exceeds this threshold value, then the control unit may activate the downhole tool or simply the valve element. This enables the downhole tool to maintain a predetermined differential pressure regardless of the operating depth, hydrostatic pressure, and mud weight. This differential pressure may also be used to determine if there is an actual flow inside the drilling string, e.g. by detecting if the first pressure is greater than the second pressure.

An object of the invention is also achieved by a circulating sub for positioning in a borehole, comprising:

-   -   a housing having an outer side surface facing an inner wall of         the borehole, where the housing is configured to be placed         inside the borehole,     -   a first fluid conduit connected to a first opening in one end of         the circulating sub and a second opening in the other end of the         circulating sub for leading a drilling fluid through the         circulating sub,     -   at least a second fluid conduit in fluid communication with the         first fluid conduit via at least one inner opening, and         connected to at least one outer opening located in the outer         side surface of the housing, characterised in that     -   at least one cavity is provided in the outer side surface of the         housing, in which at least one activation mechanism as described         above is arranged.

This provides a downhole tool with a simple and accurate activation mechanism that does not require a ball retainer for receiving one or more dropped balls, or a RF transceiver or receiver for communication with a dropped RFID tag. This reduces the complexity and number of components needed to activate the downhole tool. The activation mechanism described above allows for an activation of the downhole tool or the bypass function by means of the internal pressure of the drilling fluid only; no fluid flow is required. The downhole tool is activated by means of the pressure of the drilling fluid, this allows for a much faster activation compared to conventional indexing systems and ball or RFID tag systems.

The downhole tool comprises a central through hole, e.g. the first fluid conduit, extending from a first end, e.g. the top end, to a second end, e.g. the bottom end, for leading the drilling fluid being pumped into the drilling string through the downhole tool. The housing has a smaller diameter than the inner diameter of the borehole so that an annular is formed along the outer surface for leading the drilling fluid and cuttings back to the ground level. At least one bypass conduit, e.g. the second fluid conduit, is provided in the housing and connected to an outer opening and an inner opening for bypassing at least some of the drilling fluid.

A cavity is formed in the outer side surface in which the activation mechanism is placed. The valve element is positioned relative to the second fluid conduit and a seat located at the second fluid conduit. The seat and second fluid conduit are arranged so that the valve element, when placed in the seat, closes this fluid conduit so substantially no drilling fluid is led through the second fluid conduit. By placing the activation mechanism within the housing of the downhole tool, e.g. between the inner and outer side surfaces, the number of flow restricting elements in the fluid passageway can be reduced or even eliminated so that substantially a full-bore can be achieved, i.e. operating at maximum power or operation speed.

In one embodiment, a removable cover is arranged at an opening of the at least one cavity for closing off the at least one cavity, wherein an optional seal is provided between said cover and the housing.

The cavity is closed off by means of a cover or hatch for preventing drilling fluid or cuttings from entering the activation mechanism and potentially causing a failure in the activation mechanism. The cover and surfaces of the cavity define the chamber in which the activation mechanism is arranged. The cover/hatch may be fastened to the outer side surface by suitable fastening means, such bolts, screws, a snap-fit coupling or another arrangement. A seal or sealing element, e.g. a rubber element, an O-ring or another suitable seal, may be arranged between the cover/hatch and the housing for sealing off the chamber. This allows for easy access to the activation mechanism in the event of servicing or replacement of the activation mechanism. This also allows for a fast and simply installation of the activation mechanism as the activation mechanism can be assembled and installed as a single unit. Furthermore, no sealing elements have to be guided into and then installed inside the internal hole in which the valve element is situated. This significantly reduces the installation time and complexity thereof. This also eliminates the need for a specialised insertion tool to position the sealing elements inside the internal hole.

One or more balancing arrangements, e.g. balance pistons, may be located at the top end or bottom end of the downhole tool. The balancing arrangement may be configured to regulate or balance the pressure inside the downhole relative to the pressure of the drilling fluid located above or below the downhole tool.

In one embodiment, at least one of the inner and outer openings of the second fluid conduit comprises a nozzle configured to regulate the speed of the drilling fluid entering or exiting the second conduit.

Two or more outer openings may be arranged in the outer side surface for distributing the bypassed fluid and/or optimizing the bypass of drilling fluid. The outer openings may form branches of the same fluid conduit or different fluid conduits as described above. Alternatively, two or more cavities may be arranged in the outer surface for receiving and holding two or more activation mechanisms which each is arranged relative to at least a second or third fluid conduit.

A nozzle is provided at the inner and/or outer opening of the second fluid conduit for regulating the speed of the drilling fluid. An inner/first nozzle may be configured to increase the speed of the drilling fluid entering the conduit. An outer/second nozzle may be configured to further increase the speed of the drilling fluid exiting the conduit. The nozzles may be placed at a predetermined angle relative to the longitudinal direction of the downhole tool, e.g. in an angle of 90 degrees or in an acute angle where the nozzle at least partly faces the first/top end of the downhole tool. The nozzles may be mounted at the openings or integrated into the openings. The nozzles may be made of a wear resistant material, such as tungsten carbide or another suitable material. This allows the pressure of the drilling fluid inside the drilling string to be reduced as well as an increase in the flow of the circulating drilling fluid, if needed. The increase in the flow in the annular space may be used to dissolve or break up any packed off areas or remove accumulated cuttings from areas likely to get packed off or blocked by the cuttings, such as the transition area between two different liners.

The inner/first nozzle may be accessed and installed from the outside through a selective conduit in the housing. This selective conduit may be a separate conduit or one of the fluid conduits for bypassing the first fluid conduit. The selective conduit may be closed off by means of plug mounted at the outer opening. Alternatively, a nozzle for regulating the speed of the drilling fluid exiting this fluid conduit may be mounted at the outer opening. This further simplifies the installation and servicing process as all the nozzles can be accessed from outside the downhole tool. One or more of these bypass conduits may thus be used for multiple purposes.

The downhole tool may be any type of a circulating sub or packoff assembly (packoff buster) used in drilling applications in which a bypass function is desired. The circulating sub or packoff assembly may advantageously be placed in positions along the borehole where packoffs are likely to form, such as in areas where changes in the diameter of the borehole occur, e.g. at the transition area between different liners. Alternatively, the activation mechanism described above may be connected to or integrated into a jarring tool for releasing a stuck or lodged downhole tool, such as the jarring tool described in US 2012/0227970 A1.

An object of the invention is finally achieved by a method for activating a circulating sub using an activation mechanism as described above, where the method comprises the steps of:

-   -   positioning the circulating sub at a predetermined depth of a         borehole,     -   increasing a pressure of a drilling fluid located in the first         fluid conduit of the circulating sub,     -   monitoring the pressure of the drilling fluid inside the first         fluid conduit using at least one pressure sensor,     -   activating the circulating sub when a certain event is detected         using a control unit, characterised in that     -   the step of activating the circulating sub comprises moving a         valve element arranged in a chamber of the activation mechanism         from a closed position to an open position so that at least a         second fluid conduit is open for leading at least a part of the         drilling fluid through the second fluid conduit.

This provides a fast and accurate method for activating or deactivating a downhole tool without the use of balls or RFID tags being dropped into the drilling fluid. This method allows for a very fast action process compared to activation systems using balls or RFID tags. As example, the process for activating a downhole tool at a depth of about 3000 metres takes several hours, e.g. more than one hour, while the present invention enables the activation process to be completed within minutes, e.g. three minutes. Furthermore, the complexity as well as the number of components needed to activate the downhole tool can be reduced compared to conventional activation systems, thus reducing costs.

This configuration enables the downhole tool to be activated without requiring an actual flow through the downhole tool, thus allowing it to be operated in packed off boreholes or situations where no circulating flow can be established.

In one embodiment, the sensed pressure is monitored within at least one time window, and the circulating sub is activated by the control unit if it is determined that the sensed pressure has remained stable relative to at least one threshold value within the at least one time window.

This enables the downhole tool to be activated once the pressure has reached a predetermined activation level for that downhole tool or an operation mode thereof. When the control unit has determined that a stable pressure level has been detected, a control signal is sent to an actuator unit for initiating the movement of the valve element. The actuator unit then moves the valve element from the closed position where the second fluid conduit is closed to the open position where the second fluid conduit is open, or vice versa if that mode or tool is deactivated. This allows at least some of the drilling fluid to be bypassed from the first fluid conduit to a pressure chamber located inside the downhole tool or to the annular spacing located at the outer surface of the housing of the downhole tool. This also allows for an endless number of activations or deactivations without having to retrieve the downhole tool to empty a ball retainer or to reset the activation mechanism.

The control unit may continue to monitor the sensed pressure for detecting a change, e.g. a drop, in the pressure which indicates that the downhole tool or the selected operation mode has been activated. The pressure of the pumped drilling fluid may then be increased to the operation level or another activation level for another mode or downhole tool.

In one embodiment, the sensed pressure is monitored within at least a second time window, and a second downhole tool or another operation mode of the first downhole tool is activated by the control unit if it is determined that the pressure has remained stable relative to at least a second threshold value within the at least second time window.

This provides a simple and accurate method for activating or deactivating multiple operation modes of a downhole tool and/or multiple downhole tools by using the same activation mechanism or individual activation mechanisms. This configuration allows the multiple operation modes and/or multiple downhole tools to be activated/deactivated by simply regulating the pressure of the drilling fluid, no indexing system is needed. Furthermore, the operation modes and/or downhole tools can be activated or deactivated using different threshold levels as described above. The activation or threshold levels may be selected so that they do not interfere with the operation of other downhole tools of the drilling string.

The control unit may monitor vibrations sensed by at least one vibration sensor, and activate the downhole tool if excessive vibrations is detected, and/or monitor the sensed pressure for determining whether a jarring tool has been cocked or not and activate the jarring tool when a certain event is detected.

In this configuration, the downhole tool further comprises at least one vibration sensor connected to the control unit which monitors the vibrations of the downhole tool and in part the drilling string. The control unit compares the sensed vibrations to one or more threshold parameters, e.g. a reference frequency, pattern, amplitude or any other relevant parameters. If the sensed vibrations exceed the threshold parameters, then the control signal is sent to the actuator unit for moving the valve element so that the second fluid conduit is open. This allows the pressure of the pumped drilling fluid to be reduced while increasing the flow. This warns the operator at ground level that the drilling vibrations are out of range without using measure-while-drilling (MWD) signals.

In another configuration, the downhole tool is configured as a jarring tool or is connected to a jarring tool. The control unit compares the sensed pressure to one or more reset levels for determining if the jarring tool is recocked or not. The control unit may generate another control signal once the pressure reaches a selected reset level or if the sensed pressure remains stable at the reset level within another time window. The control unit may be configured to detect a drop having a predetermined amplitude and/or time length which indicates that the jarring tool has been cocked.

In one embodiment, an action circuit activates the control unit when the pressure of the drilling fluid exceeds a predetermined pressure level.

The electrical components are powered by an external or internal power source, such as a battery. Power to the electrical components is controlled by an optional activation circuit, e.g. a pressure switch, which turns on power when the pressure of the drilling fluid exceeds an activation level/the third threshold value. The control unit then switches from a sleep mode to a normal mode in which it monitors the pressure of the drilling fluid located in the first fluid conduit. The control unit activates or deactivates a selected operation mode or downhole tool if a stable pressure level has been detected as described above. The control unit enters sleep mode again and the power is turned off if once the activation or deactivation process is completed or if the sensed pressure drops below the activation level/the third threshold level. This saves power as the downhole tool is only activated at a predetermined pressure level, thereby reducing the power consumption and increasing the operation time.

DESCRIPTION OF THE DRAWING

The invention is described by example only and with reference to the drawings, wherein:

FIG. 1 shows an activation mechanism according to the present invention integrated into a downhole tool seen from a top end;

FIG. 2 shows a downhole tool with three activation mechanisms seen from a top end;

FIG. 3 shows a longitudinal cross-section of the activation mechanism of FIG. 1 in a closed position;

FIG. 4 shows a longitudinal cross-section of the activation mechanism of FIG. 1 in an open position;

FIG. 5 shows an exemplary application of the downhole tool placed in a borehole in a deactivated state; and

FIG. 6 shows the downhole tool of FIG. 5 in an activated state.

In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

LIST OF REFERENCE NUMBERS

-   -   1 Activation mechanism     -   2 Downhole tool     -   3 Housing     -   4 Outer side surface     -   5 Cavity     -   6 First fluid conduit, first hole     -   7 Second fluid conduit     -   8 Inner opening     -   9 Inner surface     -   10 Inner wall of borehole     -   11 Pressure sensor     -   12 Control unit     -   13 Pressure switch     -   14 Actuator unit     -   15 Valve element     -   16 Push rod     -   17 Chamber     -   18 Valve housing     -   19 Seat for valve element     -   20 Sealing elements     -   21 Annular spacing     -   22 Top end     -   23 Bottom end     -   24 Outer opening     -   25 Plug     -   26 Cover     -   27 Drill string     -   28 Borehole     -   29 Cuttings     -   30 Transition area

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows an exemplary embodiment of an activation mechanism 1 according to the present invention. The activation mechanism 1 is integrated into a downhole tool 2 in the form of a circulating sub. The downhole tool 2 and the activation mechanism 1 are seen from a top end (shown in FIGS. 3-4) where the top end, a bottom end (shown in FIGS. 3-4) and other components of the downhole tool 2 are omitted for illustrative purposes.

The downhole tool 2 comprises a housing 3 configured to be placed in a borehole where an outer side surface 4 of the housing 3 faces an inner wall (shown in FIGS. 3-4) of the borehole. A cavity 5 is formed in the outer surface 4 for receiving and holding the activation mechanism 1. The cavity 5 is closed off by a cover (shown in FIGS. 3-4) so the drilling fluid in the borehole does not come into contact with the electrical components.

A first hole 6 is formed inside the housing 3, e.g. at the centre, extending in the longitudinal direction of the downhole tool 2. The first hole 6 forms a first fluid conduit for leading drilling from the top end, through the downhole tool 2 and out of the bottom end.

A second hole 7 is formed in the wall of the housing 3 and forms a second fluid conduit for bypassing at least some of the drilling fluid. The second fluid conduit 7 is fluid communication with the first fluid conduit 6 via an inner opening 8 and with an annular spacing (shown in FIGS. 3-4) via an outer opening (shown in FIGS. 3-4). The activation mechanism 1 is arranged relative to the second fluid conduit 7 so that a valve element (shown in FIGS. 3-4) is able to control the fluid flow through the second fluid conduit 7.

FIG. 2 shows another exemplary embodiment of the downhole tool 2′ having three activation mechanisms 1, 1′, 1″ arranged in individual cavities 5, 5′, 5″ in the outer surface 4. Each of the activation mechanisms 1, 1′, 1″ is arranged relative to a second fluid conduit 7, 7′, 7″ for bypassing at least some of the drilling fluid in the first fluid conduit 6. The activation mechanisms 1, 1′, 1″ may each have the same or different configurations, e.g. they can be activated simultaneously or individually.

FIG. 3 shows a longitudinal cross-section of the activation mechanism 1 in a deactivated state. The activation mechanism 1 is positioned within the sidewall of the housing 3 between the outer surface 4 and an inner surface 9. The inner surface 9 faces the first fluid conduit 6. The outer surface 4 faces the inner wall 10 of the borehole.

The activation mechanism 1 comprises a pressure sensor 11 configured to sense the pressure of the drilling fluid located in the first fluid conduit 6. The pressure sensor 11 is electrically connected to a control unit 12 comprising a controller, e.g. a microprocessor, a memory unit, a communication interface for communicating with other downhole tools 2 or other external devices or tools, and other components for controlling the internal communication between the individual components of the activation mechanism 1. A pressure switch 13 configured to sense the pressure of the drilling fluid located in the first fluid conduit 6 is further connected to the control unit 12, e.g. a power unit thereof. The pressure switch 13 is configured to turn on or off power to the electrical components of the activation mechanism 1.

An actuator unit 14 in the form of a solenoid is electrically connected to the control unit 12. The actuator unit 14 is configured to control the movement of the valve element 15 by generating a magnetic field in its wires which influences a push rod 16 mechanically connected to the valve element 15. The push rod 16 is made of a magnetic conductive material, e.g. steel or a ferromagnetic material. The valve element 15 is moveably arranged inside a chamber 17, e.g. formed in the activation mechanism or the housing 3. One end of the valve element 15 is positioned inside a valve housing 18 which forms a retainer for the valve element 15. The valve housing 18 is connected to the push rod 16. The other end of the valve element 15 is configured to rest against a seat 19 arranged relative to the second fluid conduit 7 in a closed position as shown in FIG. 3, thus closing the second fluid conduit 7 so that no drilling fluid is bypassed via this conduit. This allows the drilling fluid to pass from the top end 22 of the downhole tool 2 and out of the bottom end 23 of the downhole tool 2 via the first fluid conduit 6.

One or more sealing elements 20, two is shown here, are arranged in an outer surface of the valve element 15 as shown in FIGS. 3-4, thereby forming a seal between the chamber 17 and the second fluid conduit 7. The sealing elements 20, e.g. O-rings, remain in contact with the inner surface of the chamber 17 at all times during the moving of the valve element 15. Thus, no bypass openings or peripheral edges are moved past either one of the sealing elements 20, thereby reducing the risk that the sealing elements 20 are forced out of its seat or otherwise gets damaged.

Another conduit connected to another outer opening 24 in the outer side surface 4 is arranged in the sidewall of the housing 3. The outer opening 24 of this conduit is aligned with the inner opening 8. Here this conduit is closed off by means of a plug 25. This conduit provides access to the inner opening 8 and allows for the installation of a nozzle as shown in FIGS. 3-4. The plug 25 may be replaced by another nozzle, thus allowing this conduit to acts as another second fluid conduit 7 for bypassing the first fluid conduit 6.

The chamber 17 is closed off by means of a remove cover 26 which secured to the housing 3. The cover 26 is sealed off using suitable sealing means to prevent drilling fluid from entering the chamber 17.

FIG. 4 shows the activation mechanism 1 in an activated state where the actuator unit 14 is activated to move the valve element, e.g. in the longitudinal direction, from the closed position shown in FIG. 3 to an open position as shown in FIG. 4.

The actuator unit 14 is configured to retract the valve element 15 further into the chamber 17 so that the other end of the valve element 15 is brought out of contact with the seat 19. This opens the second fluid conduit 7, thus allowing at least some of the drilling fluid to bypass the first fluid conduit 6 and enter the annular spacing 21. This allows the drilling fluid to pass from the top end 22 of the downhole tool 2 and to partly bypass the first fluid conduit 6 via the second fluid conduit 7.

FIGS. 5-6 show an exemplary application of the downhole tool 2 with the activation mechanism (shown in FIG. 3-4) installed in a drill string 27 or borehole assembly (BHA) which is positioned in a borehole 28. In exemplary embodiment, the downhole tool 2 is positioned above an under-reamer and/or a drill bit which are configured to widen the borehole and/or extend the borehole.

Cuttings 29 are led towards the top of the borehole 28 via the annular spacing 21 between the drill string 27 and the inner wall 10 of the borehole (here indicated by dotted lines). The cuttings 29 accumulate in the transition area 30 at which the speed of the returning drilling fluid containing the cuttings 29 is slowed down, e.g. due to a widening of the inner diameter of the borehole 28. This causes the cuttings 29 to form a packoff as shown in FIG. 5.

The activation mechanism 1 and thus downhole tool 2 remains inactive until the pressure switch 13 turns on power to the electrical components, including the control unit 12. Drilling fluid is then led through the first fluid conduit 6 and back up via the annular spacing 21 as indicated by the arrows in FIGS. 3-4.

The pressure switch 13 is activated when the internal pressure inside the first fluid conduit 6 exceeds a predetermined pressure level. The control unit 12 then wakes up and monitor the internal pressure inside the first fluid conduit 6 within one or more predetermined time windows. If the control unit 12 determines that the pressure has remained stable within at least one time window, a control signal is generated and is sent to the actuator unit 14. The actuator unit 14 then moves the valve element 15 from the closed position to the open position, thus allows at least some of the drilling fluid to bypass the first fluid conduit 6. This activates the downhole tool 2 and drilling fluid is led through the second fluid conduit 7 (indicated by arrows in FIG. 6) and out into the annular spacing 21. This increases the speed of the returning drilling fluid, thereby forcing the packoff to break up so that circulation of the drilling fluid can be resumed.

The present invention is not limited to the illustrated embodiment or the described embodiments herein, and may be modified or adapted without departing from the scope of the present invention as described in the patent claims below. 

1. An activation mechanism for activating a circulating sub in a drill string, comprising: at least one sensor configured to sense at least a pressure of a drilling fluid located in a first fluid conduit in the circulating sub when installed, a control unit connected to the sensor and configured to monitor the sensed signal of the at least one sensor, wherein the control unit is configured to electronically activate the movement of at least one moveable valve element in one direction based on the sensed signal, wherein the at least one valve element is configured to be arranged relative to at least a second fluid conduit in the circulating sub when installed, the at least one valve element is configured to move between an open position and a closed position, wherein the second fluid conduit is in fluid communication with the first fluid conduit, and the at least one valve element comprises at least one valve end configured to close the second fluid conduit in the closed position and to open the second fluid conduit in the open position, wherein the control unit is electrically connected to at least one actuator unit arranged relative to the at least one valve element, the at least one actuator unit is configured to perform a reciprocating movement of the at least one valve element an endless number of times between the open position and the closed position, wherein the control unit is further configured to electronically activate the movement of the at least one moveable valve element in an opposite direction an endless number of times.
 2. An activation mechanism according to claim 1, wherein the control unit is configured to apply at least a first time window to the sensed signal and to determine whether the sensed signal remains stable relative to at least a first threshold value within the at least first time window or not, where the at least one valve element is activated if a stable pressure level is detected.
 3. An activation mechanism according to claim 1, wherein the actuator unit comprises at least one solenoid element for inductively moving at least one push rod mechanically connected to the at least one valve element.
 4. An activation mechanism according to claim 1, wherein the at least one valve element is a poppet valve arranged inside a chamber of the activation mechanism, wherein the poppet valve is configured to move relative to the chamber when activated.
 5. An activation mechanism according to claim 4, wherein at least one sealing element is arranged in an outer surface of the poppet valve, the outer surface is facing an inner surface of the chamber, wherein the at least one sealing element remains in contact with the inner surface during movement of the poppet valve.
 6. An activation mechanism according to claim 4, wherein a valve housing is arranged inside the chamber, wherein the poppet valve extend at least partly into the valve housing via an opening in one end of the valve housing.
 7. An activation mechanism according to claim 1, wherein the control unit is further connected to activation circuit, e.g. a pressure switch, which is configured to activate the control unit at a predetermined pressure level.
 8. An activation mechanism according to claim 1, wherein the activation mechanism is configured to be implemented in a cavity located in an outer side surface of a housing of the circulating sub.
 9. An activation mechanism according to claim 1, wherein the at least one sensor comprises a first sensor configured to sense a first pressure of the drilling fluid in the first fluid conduit and a second sensor configured to sense a second pressure of the drilling fluid in a returning drilling fluid when installed, wherein the control unit is configured to determine a differential pressure using the first and second pressures.
 10. A circulating sub for positioning in a borehole, comprising: a housing having an outer side surface facing an inner wall of the borehole, where the housing is configured to be placed inside the borehole, a first fluid conduit connected to a first opening in one end of the circulating sub and a second opening in the other end of the circulating sub for leading a drilling fluid through the circulating sub, at least a second fluid conduit in fluid communication with the first fluid conduit via at least one inner opening, and connected to at least one outer opening located in the outer side surface of the housing, wherein at least one cavity is provided in the outer side surface of the housing, in which at least one activation mechanism according to claim 1 is arranged.
 11. A circulating sub according to claim 9, wherein a removable cover is arranged at an opening of the at least one cavity for closing off the at least one cavity, wherein an optional seal is provided between said cover and the housing.
 12. A circulating sub according to claim 10, wherein at least one of the inner and outer openings of the second fluid conduit comprises a nozzle configured to regulate the speed of the drilling fluid entering or exciting the second conduit.
 13. A method for activating a circulating sub using an activation mechanism according to claim 1, where the method comprises the steps of: positioning the circulating sub at a predetermined depth of a borehole, increasing a pressure of a drilling fluid located in the first fluid conduit of the circulating sub, monitoring the pressure of the drilling fluid inside the first fluid conduit using at least one pressure sensor, activating the circulating sub when a certain event is detected using a control unit, wherein the step of activating the circulating sub comprises moving a valve element arranged in a chamber of the activation mechanism from a closed position to an open position so that at least a second fluid conduit is open for leading at least a part of the drilling fluid through the second fluid conduit.
 14. A method for activating a circulating sub according to claim 13, wherein the sensed pressure is monitored within at least one time window, and the circulating sub is activated by the control unit if it is determined that the sensed pressure has remained stable relative to at least one threshold value within the at least one time window.
 15. A method for activating a circulating sub according to claim 13, wherein an action circuit activates the control unit when the sensed pressure of the drilling fluid exceeds a predetermined pressure level. 